Production of curled yarn



Feb. 13, 1962 P. VAN DIJK 3,020,700

PRODUCTION OF CURLED YARN Filed March 4. 1959 INVENTOR. PIETER VAN DIJK TO NEY Patented Feb. 13, 1962 3,020,700 PRODUCTION OF CURLED YARN Pieter van Dijk, Velp, Netherlands, assignor to Ameri This invention relates generally to the production of curled yarn or thread from thermoplastic polymerization or polycondensation products and more particularly to a process for false twisting and heat setting thermoplastic yarn.

The aforesaid false twist-heat set system is well known in the production of the curled or stretch yarn under consideration. An example of one such system may be found in US. Patent No. 2,790,298, issued to A. Kunzle. With the more conventional type yarn curling apparatus, yarn is usually fed at a controlled rate of speed into a twisting zone consisting of a twist stop or barrier, heating means, and false twister. The false twist device imparts a temporary twist to the yarn, which twist runs longitudinally of the yarn in the direction of supply through the heater, within which the twist is partially trapped or set. Upon passage out of the twisting zone, the yarn retains at least an inherent tendency to untwist, which produces the curled product desired. It is necessary in this system that the rate of withdrawal of yarn from the twisting zone be sufiiciently less than the rate of infeed to compensate for the shrinkage due to the false twist-heat set operation. Further discussion of the principles involved herein may be obtained by reference to prior patents on this subject, such as that mentioned above.

The yarn withdrawal or discharge mechanism of known curled yarn producing machines usually is driven at a speed up to about 5% slower than the infeed or supply rollers. The false twist device usually consists of a low friction type yarn encircling member, such as a freely rotatable roller or wire guide. As a result of the low friction imparted in the false twister very little, if any, tension could be developed heretofore by the discharge rollers. As a matter of fact, it was felt that no appreciable tension was necessary at this stage of the operation. Consequently, the measure of yarn shrinkage in the false twisting zone heretofore was equal to the difference in speed between the supply and discharge rollers, which as stated above amounted to less than 5%.

Although the known systems described supra operate satisfactorily in some respects, there are disadvantages concomitant therewith. It has been found that yarn passes through the twisting zone in an unsteady or nonuniform manner. It was assumed that this irregular movement of yarn resulted from the combined low tensional force of the false twist device and a high torsion couple in the non-stretched yarn, and to the tendency of yarn kinking made possible thereby. These characteristics also appeared to explain the unequal distribution of twist and curling.

One of the objects of this invention is to provide a system for curling thermoplastic yarn not having disadvantages of known processes and apparatuses.

Another object of the present invention is to provide an improved process for curling thermoplastic yarn.

Still another object of this invention is to provide a process for imparting high permanent elasticity to thermoplastic yarn during the curling thereof.

A further object of the present invention is to provide a process for producing a curled thermoplastic yarn characterized by increased permanent elasticity, more wooly appearance and improved hand when woven into fabric.

Other objects and advantages will become apparent upon study of the following detailed explanation of this invention.

In order to obviate the disadvantages of commercial systems discussed above, it has been proposed to drive the discharge rollers at a higher speed than that of the supply rollers in order to impart a yarn stretch of up to 20% of the original length. Surprisingly enough, it has now been found that the same results may be obtained without any difiiculty if the yarn passing through the twisting zone is subjected to a greater shrink than heretofore considered. This shrinkage may be reduced subsequently by means to be described hereinbelow so that the overall or final length of curled yarn has the desired ratio to original length. It has been found that this initial shrinkage imparted in the twisting zone should be at least 7%, with the upper limit being in the neighborhood of 14%. As stated earlier, the twisting zone is defined at the entrance end by the twist stop, or supply rollers if no separate twist stop is utilized, and at the discharge end by an encircling member on the false twist device.

Although it is possible to tension the yarn at least to some extent both before and after passage through the false twist device by using an encircling member C011". sisting of a small thread guiding roller, it has proved advantageous, insofar as yarn quality is concerned, to tension the yarn appreciably after passage of the same through the twisting mechanism. For best results, suflicient tension must be imparted by the falst twist device to permit stretching during withdrawal. In other words, sufiicient friction or drag resistance must be imposed on the yarn by the twisting device to snub the same and in effect to separate the system into two zones, one for shrinking the twisted yarn and another in which the shrunk yarn is partially stretched. This stretch should be such that the 7% shrinkage discussed above is reduced to between 2 and 4% when compared to the yarn originally supplied to the twisting zone.

In accordance with the present invention, yarn is passed through a twisting zone, and consequently maintained in a twisted condition, heat set and shrunk at least 7 and stretched during withdrawal from the twisting zone so that the final length is only between 2 and 4% less than the original length of yarn supplied. *In order to develop that tension at the twisting zone necessary to permit stretching by the discharge or withdrawal rollers, it has been found that the yarn should be guided under considerable tension through an encircling member immovably connected to the false twist device. This encircling member may consist of various hooks or rods in combination with thread guiding eyelets, but preferably consists of an elongated sapphire tube provided with a longitudinal bore extending transversely to the false twist spindle axis and rigidly secured thereto. Yarn to be curled is passed at least twice through the longitudinal bore, thereby encircling the sapphire wall thereof at least once. As a result of this encircling, the tension in yarn fed to the false twister is increased by a factor of between 200 and 400% upon withdrawal therefrom.

Although the false twisting device, per se, is described in US. Patent No. 2,855,750, owned in common with this application, this twister has not been used heretofore in the novel combination or for the purpose set fourth herein, insofar as known to applicant.

For a further explanation of this invention, attention is now directed to the drawing, wherein the figure is a perspective view of apparatus suitable for producing the improved product, and showing the manner in which thermoplastic yarn is threaded therethrough.

In the drawing, thermoplastic yarn 10, produced from either polymerization or polycondensation products, is withdrawn from supply pirn or package 11 by feed roller 12 and fed to a twist stop or barrier consisting of idler rollers 13, 13. The rollers 13, 13, which of course could be other type tensioning means such as one or more rods, prevent twist imparted to the yarn by the false twister presently to be described from backing up into the immediately preceding zone. Thus, these rollers form the entrance into the twisting zone mentioned earlier. Pressure roller 14 urges yarn into contact with the feed roller 12 in a manner known to this art. After passage through twist stop 13, 13 yarn 10 is fed or passed into heating means 15 which may be of known construction. The heater shown is of the electrical variety and suitable leads have been illustrated for connection to a source of current, not shown.

From heater '15 the yarn passes into the longitudinal spindle bore of false twist device generally indicated at 16. At the discharge end of the spindle bore, the yarn is passed at least twice through the bore of a sapphire encircling body or member, which bore extends normal to the axis of the spindle. The spindle is driven by direct contact with belt 17, as fully described in said Patent No. 2,855,750. It is obvious, of course, that other twisting spindles utilizing a high friction yarn contact surface could be used. Moreover, although the space between the encircling member and the twist stop 13, 13 is generally considered as the twisting zone, it is evident that the yarn discharging from this encircling member will contain an equal amount of twist as that present in the twisting zone, but in the opposite direction.

Yarn 10 is passed from the twisting device through thread guiding eyelet 18 and then onto idler roller 20, after which it is led to thread discharge or withdrawal rollers 21, 22. The curled yarn is collected on ring twisting mechanism 23, although a fiat take-up could be provided if necessary or desired.

The speed of withdrawal rollers 21, 22 should be selected so as to be between 2 and 4% lower than the speed of feed or supply rollers 12, 14. The temperature of heater 15 should be suflicient to shrink the false twisted yarn contained between the encircling member and twist stop by at least 7%. Inasmuch as the yarn in the twisting zone will be overshrunk, so to speak, it is apparent that the same must be stretched between idler roller and the withdrawal rollers in order to produce a final length of only 2 to 4% less than that supplied. Although the framework has been omitted for purposes of clarity, it will be obvious that the supply package, driven rollers, heater, false twister, guide rollers, and take up must be supported in some manner. Preferably, a common frame would be used.

The following examples elucidate specific applications of this invention.

Example I A non-oiled l4 filament yarn formed from polyamino caproic acid and having a total denier, after drawing, of 70 was spun at a rate of 900 meters per minute and cold drawn at a ratio of 2.98:1. This yarn was supplied to the curling device described above at a rate of 20.2 meters per minute and twisted by a false twist spindle with 2880 turns per meter. The yarn passed around the wall of the sapphire encircling member described by more than 540, which produced the desired tension. The sapphire member was formed by a cylindrical bead fixed with the axis thereof extending transversely to the false twist spindle axis and secured to the upper end thereof.

The yarn was heated while in twisted condition to about 170 C. by a stainless steel tube having a length of 15 cm. and an inner diameter of 0.6 mm., an electrical current of 3.1 amps. being provided for this purpose.

The shrunk, curled yarn was withdrawn from the false twist spindle at a rate of 19.6 meters per minute, which is a reduction in speed of about 2.9% from that of the infeed rollers. The twisted yarn contained within the twisting zone was thereby shrunk an amount in excess of 7% when compared to the starting length. Since the yarn had been shrunk in excess of 7%, it can be seen that the discharge rollers 21, 22 actually functioned to draw the curled yarn by about 4.1% so that the overall or final shrinkage was reduced to within the range specified hereinabove.

The yarn processed in this sample was supplied with an initial positive S-twist of about 20 turns per meter. A portion thereof was given a false twist in the S direction and another portion was given a false twist in the Z direction. The former yarn was thereafter given an additional positive twist of 195 2 per meter and the latter yarn was aftertwisted with 405 8 per meter. These two portions subsequently were corded or twisted together with 2 turns per meter. The product obtained was very elastic and other properties such as appearance, hand, etc., were very desirable.

Example [I A yarn formed from polyamino caproic acid and originally spun and drawn in the manner described above, but having a total denier of 35 after drawing and composed of only 10 filaments, was processed in a manner similar to Example I. In this example, however, the yarn was supplied at 15.9 meters per minute and withdrawn at 15.5 meters per minute, an overall shrinkage of about 2.5% resulting. The number of revolutions of the false-twisting spindle amounted to 58,000 rpm. The current in heater 15 was reduced to about 2.9 amps, but the temperature remained at because of the smaller yarn passing therethrough. Here again the initial shrinkage was in excess of 7%, but the final shrinkage was reduced to the desired range -by utilizing rollers 21, 22 to draw yarn away from the twisting spindle.

Two portions of yarn, having the same positive initial twist as discussed in Example I, were false twisted in opposite directions. The yarn twisted in the S direction Was aftertwisted with 285 2 turns per meter, and the yarn receiving the Z false twist was aftertwisted with 495 S turns per meter. These two portions were then plyed together with 125 2 turns per meter. The resulting product also was characterized by high elasticity as well as wooly appearance and hand.

It was surprising to learn that yarn produced in the manner described hereinabove had more desirable properties than that produced according to known methods. For instance, these yarns have a higher permanent elasticity, a more wooly appearance, and a better feel or hand when woven into fabric than those produced either by an overall stretch, or by a lower than 24% shrinkage between the supply and discharge devices.

Although the examples described only the use of yarn formed from polyamino caproic acid, this invention is applicable to any of the thermoplastic yarns formed from polymerization or polycondensation products. Moreover, yarns of high or low denier may be processed without difficulty.

Inasmuch as alternatives to the process and apparatus described herein will become apparent to those skilled in this art, it is intended that the scope of this invention be limited only to the extent set forth in the following claim.

What is claimed is:

A method for producing permanently curled yarn from thermoplastic products comprising the steps of supplying thermoplastic yarn to and passing said yarn through a twisting zone, snubbing the yarn to enable substantial tension increase in said tens-ion zone, twisting the yarn passing through said twisting zone while increasing the tension imparted to the yarn during twisting by between 200 and 400%, heat setting the yarn while in twisted condition sufficiently to produce yarn shrinkage of at least 7% during the heating operation, withdrawing said yarn from the twisting zone at a speed suificient to provide stretch in order to reduce the aforesaid shrinkage to between 2 and 4% with respect to the starting yarn, and collecting said 5 yarn in package form.

References Cited in the file of this patent UNITED STATES PATENTS 2,761,272 Vandamme et al Sept. 4, 1956 10 2,790,298 Kunzle Apr. 30, 1957 FOREIGN PATENTS 775,075 Great Britain May 22, 1957 1,127,005 France Aug. 6, 1956 

